Caring for the bedridden at home is one of the hardest tasks faced in elder care. More than 80 percent of the elderly currently residing in nursing homes or hospitals are there primarily because they could no longer be treated at home after having been left permanently bedridden.
Transferring the bedridden from a bed to a wheelchair is an extremely laborious, physical job, which average people are unable to perform without the use of special equipment. A variety of equipment for lifting the bedridden has been developed and deployed at both hospitals and homes. Most of the hoists, however, are awkward, uncomfortable, and often even frightening for the elderly. During the transfer, the body is not supported from beneath and tends to swing and rotate, causing great embarrassment for the patient.
Unassisted transfer from a wheelchair to a bed or a toilet requires the automated docking of a mobile unit with a fixture. Docking, or, more generally, rigid part insertion, has been performed as a part of robotic assembly tasks. Typically, rigid part insertion entails the support of the part with compliant mechanical elements or else simulating compliance through softening of servo gains. Other methods have used force sensing and active feedback such as stiffness control and impedance control.
The case of docking a personal transportation vehicle differs from typical robot assembly tasks in several crucial respects which make existing methods inapposite. First, a wheelchair is large and heavy, and has a low bandwidth and poor backdriveability. Insertion must take place slowly to avoid jerks. Furthermore, initial misalignments may be much greater than normal since the vehicle may travel long distances without course corrections. Finally, the geometric and mechanical design of the mating elements of the bed and chair may not be subject to unitary design. These considerations require a new method of force guided docking for use with an omnidirectional chair which is a subject of the present invention.